This application claims benefit of Japanese Application No. 2000-211576 filed on Jul. 12, 2000, the contents of which is incorporated by this reference.
1. Field of the Invention
The present invention relates to the structure of a lens barrel (lens frame structure) having plural frame members capable of moving back and forth relatively.
2. Description of Related Art
One known structure comprises a lens barrel having a lens frame capable of moving back and forth, a mechanism for driving a cylindrical lens frame using a combination of a cam groove run on a bias to an optical axis, and a cam-follower that engages freely with the cam groove. The whole surface of the sliding surface of the cam-follower is in contact with the sliding plane of the cam groove. This design has been used for the structure around the conjugated area of the cam-follower put in the cam groove.
The size of lens frame structure has been getting compact and thickness of the lens frame structure itself has been inclined to be thinner due to the demand for downsizing and weight saving for these products in recent years. In the event of careless stress such as impact to a cam-follower, there is a chance that the lens frame will be distorted and the engagement of the cam and the cam-follower will be pulled out. Also, in the case the cam groove has a parallel side wall, manufacturing the lens frame is difficult because the cam groove may be undercut.
To solve said problem, in the lens frame disclosed in Laid Open Patent Publication 2000-131588, one cam structure has been proposed, applying a cam groove with a V-shape in the cross-section and a cam-follower with a tapered shape. In this cam structure, the phenomenon of digging occurs due to the edge part arranged at the cam-follower with a tapered shape that makes direct contact with the cam groove plane, which is an oblique plane. This results in preventing the cam-follower from pulling out of the cam groove.
The cam structure disclosed in the Laid Open Patent Publication 2000-131588 could prevent the cam-follower and the cam groove from being pulled out by the edge caused by the cam-follower digging into the cam groove plane, which is an oblique plane. However, effecting the prevention of pulling out has not been always achieved for frame structure with extremely weak rigidity in particular, since the plane in direct contact with said edge part is an oblique plane over the area of the cam groove.
The present invention is made to resolve this problem. The object of the present invention is to provide the lens barrel using the cam mechanism with a cam-follower, where the lens barrel is capable of a smooth driving back and forth and its engaging is unlikely to be pulled out the engaging part of the cam-follower and, in addition, its frame is easy to be manufactured.
The lens barrel of the present invention comprises a first frame having a cam-follower with a conical surface part and a circular ring part where the edge is formed in the outer circumference, and a second frame having the first cam groove engaged and conjugated with sliding only with the conical surface part of the cam-follower and the second cam groove engaged and conjugated with sliding simultaneously with both the conical surface part and the circular ring part of the cam-follower.
Also, the lens barrel of the present invention comprises a first frame having a cam-follower with a conical surface part and a circular ring part where the edge is formed in the outer circumference, and a second frame having the cam groove engaged and conjugated with sliding of both the conical surface part and the circular ring part of the cam-follower.